In recent years, technologies have been developed for utilizing a variety of energy resources from viewpoint of environmental measure, saving resources and saving energy. Among them is a technology for taking out the mechanical energy from the thermal energy present in the natural world, such as solar heat. Technologies have also been developed to improve the thermal efficiency of an internal combustion engine by generating the power by utilizing the heat wasted into the exhaust gas or the cooling water of an internal combustion engine such as diesel engine, and by recovering the power.
A heat engine is used for converting the thermal energy into the mechanical energy such as rotational energy. The heat engine such as the internal combustion engine or the steam turbine that uses an ordinary fuel such as petroleum, natural gas or the like, is the one in which the fuel is burned to produce an operation fluid of a high temperature and a high pressure and the thermal energy is converted into the mechanical energy, and features a high thermal efficiency since the mechanical energy is taken out from the heat source in the state of a high temperature. However, the temperature of the thermal energy in the natural world and the exhaust heat of the internal combustion engine are, usually, not so high, i.e., these are the thermal energy in a low-temperature state. In order to efficiently take out the mechanical energy from such heat sources, therefore, it becomes necessary to use a heat engine adapted to the thermal source in a low-temperature state.
The engine disclosed in JP-A-2001-20706 is a heat engine for generating the mechanical energy from the heat source in a low-temperature state. As shown in FIG. 3, this engine comprises a heating portion 101 and a cooling portion 102 which are coupled together through nozzles 103. A turbine 106 is arranged in the cooling portion 102 at a position facing the nozzles 103, and rotates together with magnets 107. On the inside of the magnets 107, a stationary generating coil 110 is arranged facing thereto, and the magnets 107 and the generating coil 110 together constitute a generating device. The heating portion 101 and the cooling portion 102 are sealed, respectively. Water 104 which is an operation fluid is filled therein, and the air inside is evacuated by a vacuum pump. Many heat pipes 105 are mounted on the upper side of the cooling portion 102 to radiate the heat.
The heating portion 101 and the cooling portion 102 as a whole constitute a heat pipe, and water 104 became the steam being heated in the heating portion 101 from the lower side thereof creates a high-speed stream which is jetted to the blades of the turbine 106 from the nozzles 103. Therefore, the turbine 106 and the magnets 107 rotate to produce the rotational energy which is, finally, converted into the electric energy by the magnets 107 and the generating coil 110, and is output to an external unit. The steam after having driven the turbine 106 is cooled down with the heat-radiating action of the heat pipes 105 and returns back to water. The condensate falls down to the lower side of the cooling portion 102 due to the gravity, and is refluxed into the heating portion 101 through the central portion.
The heat pipe that utilizes the vaporization and condensation of liquid contained in the sealed container is, usually, used as a heat carrying means, i.e., as a heat transfer device. However, the steam of liquid contained in the heat pipe moves accompanying large velocity energy and, therefore, the power can be taken out therefrom as described above. In this case, the mechanical energy can be taken out from the heat source in a low-temperature state.
The turbine disclosed in the above JP-A-2001-20706 is a so-called velocity type engine which utilizes the velocity energy of the operation fluid. To efficiently operate the turbine, the rotational speed of the turbine must be increased so that the circumferential velocity thereof is increased to match the velocity of the steam. However, when decreasing the diameter of the turbine to miniaturize it, the rotational speed of the turbine becomes very high and a large centrifugal force acts on the turbine, and may break it down. Further, when the temperature of the heating portion is low and the steam is of a low temperature, the superheat of the steam is in a low degree, and water droplets tend to form due to the cooling. Water. droplets that are formed come into collision with the turbine blades at high speeds, and the so-called erosion is developed on the turbine blades due to the collision of water droplets.
When the heat engine is rotated being contained in a closed container, the rotary shaft must be supported by bearings having sealing performance. To support the rotary shaft that rotates at high speeds such as of the turbine, precision bearings are necessary. Namely, complex and expensive bearings must be used to support the rotary shaft maintaining sealing performance.